Rated 5 out of 5 stars

Very good tweak.
I just made a modification to use a checkerboard like in Photoshop instead of a transparent background.

I replaced in resources/transparent-standalone-images/lib/main.js "none" by url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAMAAAAoLQ9TAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAAZQTFRF////zMzMOOqqgwAAABdJREFUeNpiYIQCBhgYIIEBth4mABBgAEUQAIEfdL0YAAAAAElFTkSuQmCC')

I wanted to do it with useChrome.css as suggested by no luck...

This review is for a previous version of the add-on (initial.rev29.1-signed.1-signed).